1. Field of the Invention
This invention relates to a cylinder, a load port using it and a production system using the load port, and in particular, to a load port which complies with the SEMI standard and copes with FOUPs (Front Opening Unified Pods) having a variety of latchkey receptacle shapes.
2. Description of the Related Art
Until now, open cassettes have been mainly used as a container which stores a plurality of semiconductor wafers. However, in order to reduce the production cost of high-characteristic semiconductor devices, the mini-environment systems have been advocated, which reduce the cost related to a clean room. In the mini-environment systems, the SMIF (Standard Mechanical Interface) system is widely used for 200 mm-wafers, and the FOUP (Front Opening Unified Pod) system is being examined to be used for 300 mm-wafers.
The FOUP system was advocated and provisionally standardized at SEMI (Semiconductor Equipment and Materials International) composed of semiconductor manufacturing equipment manufacturers and material manufacturers all over the world. Semiconductor device manufacturers are also preparing to construct the mass-production line with this system. The FOUP system was technically examined at the standard committee of SEMI and was provisionally standardized. Here, the SEMI standard E57-0299 strictly defines the accuracy of the load port mechanical interface method to open and close an FOUP door; on the other hand, it allows FOUP manufacturers more latitude in adopting mechanical interface of FOUP.
The FOUP system, for example, is described in detail in JP8-279546A. The structure and the opening and closing mechanism of FOUP are explained by referring to FIGS. 5 and 6. FIG. 5 is a perspective view of a load port carrying out the opening and closing of FOUP door. Here, load port 30 is composed of frame 31 having a opening, stage 32 which is enable to move in the frame direction and has three kinematic pins 34 on the surface, and port door 33 which is inserted into the opening from opposite direction to stage 32 and retreated from the opening. In port door 33, two registration pins 36 are mounted diagonally, and two latchkeys 35 that rotate between the vertical position (90-degree position) and the horizontal position (0-degree position) are installed. Additionally, holding pads 37 are installed surrounding respective registration pins 36 to fix FOUP door 52 to port door 33.
FOUP 50 is composed of FOUP box 51 and FOUP door 52, as is shown in FIG. 6. FOUP box 51 has a plurality of shelves to hold wafers 53 and handles 56 for carrying by hand. In FOUP door 52, latch holes 55 and registration holes 54 are formed at corresponding positions to latchkeys 35 and registration pins 36 of port door 33. Inside latch holes 55, a latchkey receptacle is installed to engage with latchkey 35. The locking and unlocking operation of latches 56 is carried out by turning the latchkey receptacles using the latchkeys.
It is stipulated in the SEMI standard that fixing and unfixing of FOUP door 52 to and from FOUP box 51 is made by turning the latchkey receptacles to the positions of the 90-degree and the 0-degree, respectively. However, there is no concrete stipulation on the fixing method of FOUP door, and therefore, FOUP manufacturers are allowed to adopt their own method. The opening and closing mechanism of Foup door is described in, for example, U.S. Pat. No. 5,915,562.
The opening and closing operation of FOUP will be explained below. An FOUP is placed on stage 32 having three kinematic pins 34 mounted thereon and is aligned with the aid of the kinematic pins. Then, stage 32 is moved forwards to insert registration pins 36 of the port door into registration holes 55 of FOUP 50, whereby the FOUP door is positioned against the port door. Further advance of the stage makes latchkeys 35 of the port door engage with latchkey receptacles through latch holes 55 of FOUP, and the FOUP door finally contacts with the port door. At this stage, the inside of holding pads 37 installed around the root of registration pins 36 are evacuated to fix the FOUP door to the port door.
Then, the FOUP door is detached from the FOUP box by turning latchkeys 90 degrees to the 0-degree position. The port door, holding the FOUP door, is moved backwards and then downwards. Thus, wafers can be taken out through the opening. Each wafer stored in the FOUP box is transferred by e.g. a scalar type robot disclosed in JP No. 2749314 to a wafer processing tool.
When the FOUP door is closed, the same operation is made in reverse order.
This FOUP system was established as a provisional specification of SEMI in 1996, and each company has developed and manufactured FOUPs and load ports on the basis of this standard. Various disadvantages about the FOUP system have been clarified with advancing the verification of operation.
As mentioned above, there is few stipulation on FOUP, in spite of strict stipulation on the load port: for example, the shape and size of latchkey are defined including their tolerance, but those of latchkey receptacle are not. Therefore, the following problems have arisen. According to the SEMI standard E62-0999, the tolerance on the rotation angle of latchkey is defined as ±1 degree at the 0-degree position and 90-degree position. However, since there is no stipulation on the size of the latchkey receptacle, latchkey receptacles may not rotate 90 degrees even if latchkeys rotate by 90 degrees, as shown in FIG. 13, in the case where the width W1 of latchkey receptacles 57 is to some extent larger than the width W2 of latchkey 35. That is, latchkey receptacles may not rotate to the 90-degree position, but to the (90-θ) degree position depending on the difference of (W1-W2), which results in failing to lock the latches. Even when the latches are locked, if the FOUP of which latch receptacles do not stay at the 90-degree position is transported to the load port of next process tool and the stage thereof is moved forwards to open the FOUP, latchkeys may contact or collide with latchkey receptacles of the FOUP. The contact or collision makes dust, and contaminates the wafer transferring space. Furthermore, the repetition of the contact and collision may deform the latchkey receptacles, resulting in that latchkey receptacles cannot rotate to the 0-degree position, even when latchkeys rotate to the 0-degree position. Thus, latchkeys will stop at e.g. 5 degrees that is out of tolerance range of ±1 degree, which means that the FOUP door can not be detached from FOUP box. This becomes severe disadvantage in the manufacturing process.
Although each FOUP manufacturer has carried out various examinations in order to solve the above problems, the appropriate solution has not been obtained from the viewpoint of cost and reliability.